Human immunodeficiency virus (HIV) is a retrovirus which is the etiological agent of acquired immunodeficiency syndrome (AIDS) and its precursor AIDS-related complex (“ARC”), a syndrome characterized by symptoms such as persistent generalized lymphadenopathy, fever and weight loss. AIDS is characterized by the destruction of the immune system, particularly CD4 T-cells, with attendant susceptibility to opportunistic infections. A common feature of retrovirus replication is the extensive post-translational processing of precursor polyproteins by a virally encoded protease to generate mature viral proteins required for virus assembly and function. Inhibition of this processing prevents the production of normally infectious virus. For example, Kohl et al. (Proc. Natl Acad. Sci. 85: 4686-4690 (1988)) demonstrated that genetic inactivation of the HIV encoded protease resulted in the production of immature, non-infectious virus particles. These results indicated that inhibition of the HIV protease represents a viable method for the treatment of AIDS and the prevention or treatment of infection by HIV.
The HIV genome is made up of single-stranded RNA which comprises several genes that code for structural proteins common to all retroviruses and additional genes that code for accessory proteins specific to HIV (A. D. Frankel and J. A. T. Young, Annu. Rev. Biochem. 67:1-25 (1998)). Open reading frames encoding structural proteins include the pol gene (Ratner et al., Nature 313: 277-284 (1985)), which encodes reverse transcriptase, integrase and HIV protease, the gag gene, which encodes the core proteins of the virion (Toh et al., EMBO J. 4: 1267-1272 (1985); Power et al., Science 231: 1567-72 (1986); Pearl et al., Nature 329: 351-54 (1987)), and the env gene, which encodes gp120 (surface) and gp41 (TM/transmembrane).
Several HIV protease inhibitors are presently approved for clinical use in the treatment of AIDS and HIV infection, including indinavir (see U.S. Pat. No. 5,413,999), amprenavir (U.S. Pat. No. 5,585,397), saquinavir (U.S. Pat. No. 5,196,438), ritonavir (U.S. Pat. No. 5,484,801) and nelfinavir (U.S. Pat. No. 5,484,926). Each of these protease inhibitors is a peptide-derived peptidomimetic, competitive inhibitor of the viral protease which prevents cleavage of the HIV gag-pol polyprotein precursor. Tipranavir (U.S. Pat. No. 5,852,195) is a non-peptide peptidomimetic protease inhibitors also approved for use in treating HIV infection. The protease inhibitors are administered in combination with at least one and typically at least two other HIV antiviral agents, particularly nucleoside reverse transcriptase inhibitors such as zidovudine (AZT) and lamivudine (3TC) and/or non-nucleoside reverse transcriptase inhibitors such as efavirenz and nevirapine. Indinavir, for example, has been found to be highly effective in reducing HIV viral loads and increasing CD4 cell counts in HIV-infected patients, when used in combination with nucleoside reverse transcriptase inhibitors. See, for example, Hammer et al., New England J. Med. 337: 725-733 (1997) and Gulick et al., New England J. Med. 337: 734-739 (1997).
The established therapies employing a protease inhibitor are not suitable for use in all HIV-infected subjects. Some subjects, for example, cannot tolerate these therapies due to adverse effects. Many HIV-infected subjects often develop resistance to particular protease inhibitors. Accordingly, there is a continuing need for new compounds which are capable of inhibiting HIV protease and suitable for use in the treatment or prophylaxis of infection by HIV and/or for the treatment or prophylaxis or delay in the onset or progression of AIDS.